THE US Office of Personnel Management (OPM) acted illegally when it ordered the mass sackings of probationary workers as part of President Donald Trump’s drive to shrink the federal workforce, according to a court decision reported on Monday.

Awarding judgement to a coalition of trade unions and not-for-profit organisations, US District Judge William Alsup of San Francisco said on Friday that the human resources office had “unlawfully exceeded its own powers and usurped and exercised powers reserved by Congress to each individual” federal agency to hire and fire its own workers.

He rejected the government’s claim that the office did not direct employment decisions but merely offered guidance to other agencies.

“Judge Alsup’s decision makes clear that thousands of probationary workers were wrongfully fired, exposes the sham record the government relied upon and requires the government to tell the wrongly terminated employees that OPM’s reasoning for firing them was false,” American Federation of Government Employees national president Everett Kelley said in a statement.

The office did not respond to a request for comment on Monday.

More than 25,000 probationary workers were terminated soon after Mr Trump took office in January.

Mr Alsup said too much time had passed for them to reinstated.